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Inequalities in CVD

There have been consistent findings about ethnic inequalities in cardiovascular disease. However, what causes the increased occurrence of cardiovascular disease for some ethnic groups is still not well understood. Effort has been made to investigate the underlying reasons of ethnic inequalities in cardiovascular disease from different perspectives, including classical risk factors, novel risk factors, gene-environment interactions, racial discrimination and socioeconomic status, although little is known to what extent these factors contribute to ethnic inequalities in cardiovascular disease.

The prevalence of classical causal factors, such as high blood pressure, diabetes mellitus, insulin resistance, obesity and physical inactivity, is comparatively high in minority ethnic groups, which might account for part of the observed ethnic disparities (Cappuccio et al., 1997, Primatesta et al., 2000, Ehtisham et al., 2005,

factors, specifically lipoprotein(a) or Lp(a) (Bhatnagar et al., 1995, Anand et al., 1998), C-reactive protein (CRP) (Danesh et al., 2004, Forouhi et al., 2001), fibrinogen (Kain et al., 2001) and homocysteine (Chambers and Kooner, 2001). Migration was identified to be an important factor in determining the increased risk of coronary heart disease of immigrants due to changes in dietary patterns and lifestyles, known as adverse gene-environment interactions (Bhatnagar et al., 1995, Khunti and Samani, 2004, Patel et al., 2006). However, the migration explanation might not be applicable to the second or third generation of immigrant population. In addition, racial discrimination is argued to be a central component of ethnic inequalities in health, which refers to personally perceived bias that occurs between individuals, or discriminatory policies or practices of organizations that result in differential access to resources and societal opportunities (Williams et al., 2003, Karlsen and Nazroo, 2002, Krieger, 2000). However, because racial discrimination is hard to measure and no data about it are available, little quantitative research has examined the contribution of racial discrimination to ethnic inequalities in cardiovascular disease.

Given that in the UK, people from most minority ethnic groups are associated with lower socioeconomic status (which is introduced in Chapter Two) and that there are established well-known relationships between socioeconomic status and health, ethnic inequalities in health might be explained by socioeconomic inequalities among ethnic groups. Indeed, the contribution of socioeconomic inequalities to ethnic inequalities in health has been much debated over the last three decades with inconsistent conclusions about whether socioeconomic inequalities are the fundamental causes of ethnic inequalities in health.

The Black Report, which was published in 1980 by the Department of Health and Social Security (now the Department of Health) in the UK, has suggested four possible explanations for the existence of health inequalities between social classes in Britain, including artefact, natural or social selection, cultural/behavioural factors and materialist/structural explanations. The latter one placed emphasis on the role of

economic and associated socio-structural factors, including poverty, poor housing conditions, poor conditions of work and lack of resources in health and education, in distribution of health and well-being (Townsend and Davidson, 1982). This would suggest that socioeconomic factors might also be relevant to ethnic inequalities in health.

However, Marmot et al. (1984a) don’t consider socioeconomic gradient to be an important factor for ethnic inequalities in health. In an examination of migrant mortality statistics for 1970-1978 in England and Wales, socioeconomic gradient was found unrelated to higher mortality rates for most migrant groups. For people born in the Caribbean, there was even an association between higher socioeconomic status and higher mortality. Marmot et al. concluded that: “(a) differences in social class distribution are not the explanation of the overall different mortality of migrants; and

(b) the relation of social class (as usually defined) to mortality is different among

immigrant groups from the England and Wales pattern.” The analysis of recent migrant mortality statistics for 1991-1993 in England and Wales also suggested that socioeconomic differences, as measured by social class, didn’t explain the different rates of mortality between groups born in different countries (Harding and Maxwell, 1997).

Nazroo (1998, 2003a, 2003b) suggested that social and economic inequalities were fundamental causes of ethnic inequalities in health by analyzing the Fourth National Survey of Ethnic Minorities (1993-1994), which is a nationally representative survey of ethnic minority and white people living in England and Wales. Topics in The Fourth National Survey of Ethnic Minorities include economic position, education, housing, health, ethnic identity, and experiences of racial harassment and discrimination. The contribution of socioeconomic effects to ethnic inequalities in health had been investigated for three broad ethnic minority groups (Indian or Africa Asian, Bangladeshi or Pakistani, Caribbean) and six different health outcomes. After

ethnic groups reduced to some extent. The importance of socioeconomic inequality to ethnic differences in the reporting of fair or bad general health was also reported in the same papers based on the Health Survey for England 1999. A clear reduction in odds ratios for most minority ethnic groups was identified when adjusting for socioeconomic status measures (income, housing tenure, economic activity). However, in both of the two pieces of evidence, socioeconomic inequalities can’t fully explain ethnic inequalities in health.

Chandola (2001) did a similar study but with a slightly different conclusion. The author investigated the contribution of socioeconomic status to inequalities in self-rated health among a White group, an Indian group, and a combined Pakistanis and Bangladeshis group based on The Fourth National Survey of Ethnic Minorities (1993-1994) as well, using a new measure of socioeconomic status, the National Statistics Socioeconomic Classification (NS-SEC). The result showed that after controlling for standard of living, the NS-SEC and the percentage of households within a ward without access to a car, there were no significantly higher odds of poorer health for South Asians compared to the white people. However, it was acknowledged that due to small sample size, Pakistanis and Bangladeshis were combined into a single group for analyses, and men and women were combined into a single group as well.

Cooper (2002) also addressed whether socioeconomic inequalities were a potential explanation for ethnic inequalities in self-reported health using the data of the Health Survey for England combined over 4 years from 1993 to 1996. The key finding was that, socioeconomic status, measured as educational level, employment status, occupational social class and material deprivation, was found to account for a large proportion of the inequalities in self-reported health among Black Caribbean, Pakistani and Bangladeshi groups. However, significant ethnic inequalities in health remained after controlling for socioeconomic status.

cause of ethnic inequalities in health, there are some gaps in previous studies. Firstly, most studies examined the contribution of socioeconomic status to ethnic inequalities in only one measure of health, self-reported health, using the two main data the Fourth National Survey of Ethnic Minorities (1993-1994) and the Health Survey for England, which may not adequately capture different dimensions of health, such as cardiovascular disease and mental health. Few studies investigated whether socioeconomic inequalities were the main cause of ethnic inequalities in cardiovascular disease, with one exception of Nazroo’s study (2001) which assessed the importance of socioeconomic position in South Asians’ higher risk of cardiovascular disease.

Secondly, ethnic groups other than Caribbean and South Asian seldom have been studied in analysis of the socioeconomic effect on ethnic inequalities in health. Furthermore, in previous studies using the Fourth National Survey of Ethnic Minorities (1993-1994), Bangladeshi and Pakistani groups were usually combined into one group, Indian and Africa Asian were combined into one group as well, due to small sample size, which ignored the heterogeneities between these groups. However, as more and more immigrants enter the UK over the last decade and the understanding of ethnic groups evolves, more ethnic groups have been identified and classified. For example, in the UK 2001 Census, there were eleven categories in the ethnicity classification, among which Black Africa, Mixed, Other Asian and Chinese groups have been less studied. For these groups, it is unknown to what extent socioeconomic inequalities contribute to ethnic inequalities in health.

One of the main objectives of this study is to investigate to what extent socioeconomic inequalities contribute to ethnic inequalities in different types of cardiovascular disease, given that subtypes of cardiovascular disease might have different risk factors and the role of socioeconomic status in subtypes of cardiovascular disease may be different. Furthermore, if ethnic inequalities in

have a contribution to the inequalities is also a question that needs investigation in this study. However, given that information about individuals’ socioeconomic status is not available in the HES, areal socioeconomic status measures have to be used, which offers an opportunity to investigate the potential of using areal socioeconomic measures for studying ethnic inequalities in cardiovascular disease when individual socioeconomic measures are seldom available in health data

Nazroo (2003a) suggested the geographical location of residence of people from minority ethnic group might be an important source of social disadvantage that determines their poor health. Karlsen et al. (2002) explored the contribution of individual level and ward level characteristics to self-reported fair or poor health among four ethnic groups (Caribbean, Indian, Pakistani and Bangladeshi, and white) in the UK based on the Fourth National Survey of Ethnic Minorities (1993-1994). On the whole, none of the ward level indicators, including the quality of the local environment, the provision of local amenities and local problems of crime and nuisance, was statistically and significantly associated with self-reported health among ethnic groups. However, the relationship between socioeconomic environment and ethnic inequalities in cardiovascular disease is less studied.

Using areal socioeconomic status measure is subject to two problems. Firstly, the ecological fallacy, which refers to the bias introduced when using areal measures alone to make inference about individual level relationships (Selvin, 1958, Firebaugh, 1978). However, there is substantial evidence based on the individual level supporting the conclusion that ecological correlations between socioeconomic deprivation and health could reflect associations among the relevant variables in individuals (MacRae, 1994). Geronimus (2006) concluded that as long as health data offer few other options, areal socioeconomic measures will continue to be used to proxy unavailable individual socioeconomic variables, with careful interpretation of study results.

that statistical results defined over a set of essentially arbitrary areal units vary according to the geographical scale at which the analysis is conducted (scale problem of the MAUP) and how the geographical boundaries are drawn at that scale (zonation problem of the MAUP) (Flowerdew et al., 2001). In order to examine how the results vary across geographical scales, the effect of areal socioeconomic status measured at different geographical scales is investigated in this study.